The invention relates to a method for operating an internal combustion engine and especially an internal combustion engine of a motor vehicle.
The invention proceeds from a method for operating an internal combustion engine, especially of a motor vehicle, wherein a plurality of cylinders is arranged in two cylinder banks and wherein each of the two cylinder banks is assigned a sensor for determining the composition of the exhaust gas and wherein a control factor for each of the two cylinder banks is determined in dependence upon the output signals generated by the two sensors. The fuel mass, which is injected into the two cylinder banks, is influenced with the control factor. The invention likewise relates to a corresponding internal combustion engine as well as a corresponding control apparatus for an internal combustion engine of this kind.
The cylinders are often arranged in two cylinder banks in multi-cylinder internal combustion engines.
The air, which is necessary for the combustion, is supplied to all cylinders via a common intake manifold. There, an air mass sensor, such as an HFM-sensor, can be provided with which the air mass inducted via the intake manifold can be measured.
Separate exhaust-gas pipes are connected at the exhaust ends to the two cylinder banks. Each of these exhaust-gas pipes is assigned a sensor which is provided for measuring the composition of the exhaust gas. If the engine is a gasoline engine, then the two sensors are conventionally realized as lambda probes.
The HFM-sensor generates an output signal which is relevant to the same extent for both cylinder banks. If the output signal is defective (for example, because of a defect of the HFM-sensor), then this effects a fault, which is independent of the cylinder bank, in the control (open loop and/or closed loop) of the engine. Other faults, which are independent of the cylinder bank, can arise, for example, because of a defective fuel pressure or the like. Such cylinder-independent faults can lead to misfires or to the standstill of the engine.
The fuel masses, which are to be injected into the two cylinder banks, are each separately computed by a control apparatus in dependence upon the output signals of the lambda probes which are arranged in the exhaust-gas pipes of the two cylinder banks. In the above-mentioned gasoline engine, respective control factors are computed in dependence upon the output signals of the two lambda probes. The control factors influence the injection of fuel into the respective corresponding cylinder banks. This control factor is usually generated with the aid of a so-called lambda controller. A separate lambda controller is assigned to each of the two cylinder banks.
Furthermore, an adaptation is assigned to each of the two cylinder banks. In this way, the control factor does not have to be used in order to compensate, for example, for deteriorations of the engine. This is corrected with the aid of the adaptation.
If one of the two sensors in the exhaust-gas pipes of the engine exhibit a malfunction, this then defines a cylinder-bank dependent fault. In this case, the lambda controller, which corresponds to the defective sensor, attempts to compensate this malfunction by a corresponding change of the control factor. The lambda controller of the intact sensor of the other cylinder bank is, however, not affected by this compensating operation.
Cylinder bank dependent faults of this kind can also arise because of other defects which always separately affect only one of the two cylinder banks.
Such cylinder-bank dependent faults can lead to the situation that the cylinder bank, which is associated with the fault, is operated with an air/fuel mixture which is much too rich. This, in turn, can lead to misfires or even to damage of the catalytic converter assigned to the cylinder bank.
In total, a cylinder-bank independent fault as well as a cylinder-bank dependent fault cause a similar reaction of the engine, namely, the misfire of cylinders. Cylinder-bank dependent and cylinder-bank independent faults cannot be distinguished or are distinguishable much too late from this reaction.
It is an object of the invention to provide a method with which the cylinder-bank dependent and the cylinder-bank independent faults can be distinguished.
The method of the invention is for operating an internal combustion engine including an internal combustion engine for a motor vehicle. The engine has a plurality of cylinders arranged in two cylinder banks and the method includes the steps of: providing first and second sensors for corresponding ones of the cylinder banks to determine the composition of the exhaust gas and the first and second sensors outputting first and second output signals (uvsk1, uvsk2); determining first and second control factors (fr1, fr2) for corresponding ones of the cylinder banks in dependence upon the first and second output signals (uvsk1, uvsk2), respectively, and the first and second control factors (fr1, fr2) being applied for influencing the respective fuel masses (ti1, ti2) to be injected into corresponding ones of the cylinder banks; comparing the control factors (fr1, fr2) to each other; and, distinguishing between a cylinder-bank independent fault and a cylinder-bank dependent fault in dependence upon the first and second control factors (fr1, fr2).
If a cylinder-bank dependent fault is present, that is, for example, one of the two sensors in the exhaust-gas pipes of the engine exhibits a fault, then this has the consequence that the corresponding lambda controller attempts to correct this fault by correspondingly influencing the fuel mass to be injected. The control factor of this lambda controller changes especially in the direction of a rich operation of the corresponding cylinder bank. For a cylinder-bank dependent fault (that is, for example, under the precondition that only one of the two sensors in the exhaust-gas pipes of the engine exhibits a fault), this has the consequence that the control factor of that cylinder bank wherein the fault or the defect of the sensor is present deviates from that control factor which belongs to the other cylinder bank. This deviation of the two control factors from each other is detected.
According to the invention, this deviation is used to distinguish between a cylinder-bank independent fault and a cylinder-bank dependent fault. In this way, a malfunction of the engine is reliably detected.
A conclusion is drawn as to a cylinder-bank independent fault especially when the two control factors do not deviate significantly from each other.
It is especially advantageous when a conclusion is drawn as to a cylinder-bank dependent fault for a significant deviation of the two control factors.
In this way, it is possible to detect a cylinder-bank dependent fault reliably and early and especially the defect of one of the two sensors in the exhaust-gas pipes of the engine. For this reason, countermeasures can already be initiated before, for example, the adaptation intervenes. The adaptation, for example, corresponds to the defective sensor.
This early detection of a fault per se as well as the early distinguishability between a cylinder-dependent and a cylinder-bank independent fault is of special significance in direct-injecting engines. In these engines, the generated torque is directly dependent upon the injected fuel mass in the so-called stratified charge operation. For a cylinder-bank dependent fault, if the corresponding lambda controller or the corresponding adaptation would undertake an enrichment of the air/fuel mixture in order to compensate for the fault, then this would have as a consequence that a larger torque is generated. This larger torque would then lead to an acceleration of the motor vehicle which is not even wanted by the driver thereof.
It is therefore of great significance that an occurring fault is detected quickly and properly corrected. This is reliably achieved by the invention for direct-injecting internal combustion engines. It is possible to rapidly initiate the proper correction of the fault with the distinguishability between the cylinder-bank dependent and the cylinder-bank independent faults. Especially for a cylinder-bank dependent fault, only the affected cylinder bank need be influenced; whereas, for a cylinder-bank independent fault, both cylinder banks have to be correspondingly corrected.
In this way, it is, inter alia, ensured that an unwanted acceleration of the engine and therefore of the vehicle does not take place.
Basically, the described invention can be utilized in gasoline as well as diesel engines. Likewise, the invention can be applied to intake-manifold injections as well as for direct injections. A condition precedent is, however, that at least a dual exhaust-gas sensor arrangement is present.
As already explained, it is, however, especially advantageous to apply the invention to an internal combustion engine having gasoline direct injection wherein a lambda controller is provided with which the air/fuel ratio, which is to be supplied to the engine, is controlled (open loop and/or closed loop) to a stoichiometric value.
An advantageous further embodiment of the invention is applicable where an adaptation for the fuel mass, which is to be injected into both cylinder banks, is carried out. Here, for a fault detected as being cylinder-bank dependent, the adaptation values of the defective cylinder bank are set to the adaptation values of the other cylinder bank. In this way, it is achieved that both cylinder banks of the engine can continue to be operated as though no basic fault were present.
Another embodiment of the invention is applicable where a tank-venting system is connected to an intake manifold of the engine and wherein a tank-venting adaptation is carried out for the fuel mass supplied via the tank-venting system. In this embodiment, for a fault detected as cylinder-bank independent, the tank-venting adaptation changes into an emergency program or, for a fault detected as cylinder-bank dependent, the tank-venting adaptation is carried out in dependence upon the cylinder bank detected as being non-defective. The tank-venting adaptation is, for example, held constant in the context of the emergency program. In this way, a defective sensor does not cause a basic change of the tank-venting adaptation. In lieu thereof, the tank-venting adaptation is carried out in such a manner that the engine including the tank venting continues to be carried out without a basic fault occurring thereby.
Of special significance is the realization of the method of the invention in the form of a computer program which is provided for the control apparatus of the internal combustion engine. The computer program can be run on a computer of the control apparatus and is suitable for executing the method of the invention. In this case, the invention is therefore realized by the computer program so that this computer program defines the invention in the same manner as the method for which the computer program is suitable for carrying out. The computer program can preferably be stored on a flash memory. A microprocessor can be provided as a computer.
Other features, application possibilities and advantages of the invention will become apparent from the description of the embodiments of the invention which follows and which are shown in the drawing. Here, all described or illustrated features by themselves or in any combination define the subject matter of the invention independently of their composition in the patent claims or their dependency as well as independently of the formulation or presentation in the description or in the drawing.